Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 157

Huang et al. explored cholesterol moiety as a hydrophobic anchor for the first
time. They synthesized (3b)-[ N -( N , N -dimethylaminoethyl)carbamoyl]cholesterol
(DC-Chol), which has gained much interest since then. Université Paris 13 Nord
presented 3-b-[ N -( N ,N,N-triethylamino propane)-carbamoyl] cholesterol (TEPAC-
Chol) and its analogues, which demonstrated better transfection efficiency in MCF7,
A549, U37MG ,and HUH7 cell lines ( Fig. 4.11 ) [208] . Megabios proposed a family
of cyclic bis-quaternary ammonium salts by the synthesis of derivatives of pipera-
zine MeBOP, DBPP, and DBOP, formulated in combination with colipid cholesterol
( Fig. 4.11 ) [209] . These formulations demonstrated comparable (MeBOP, DBOP) or
enhanced (DBPP) transfection activity in vivo as compared to (dimethyldioctadecyl-
ammonium bromide) DDAB:cholesterol.
Cationic phospholipids coformulated with DOPE or cholesterol were found
to be an effective transfection vector for in vitro as well as in vivo applications
[210,211,212] . Cationic substitution with nitrogen or phosphorus on the polar group
of this family of compounds confers a significant increase in transfection efficiency
in vitro against CFT1, K562, HT29, and Hela cell line and in vivo . Also, there was a
considerable decrease in cytotoxicity.
4.3.2 Lipoamines
Behr proposed another rational approach for DNA vectorization, which differs from
Felgner's quaternary ammonium salt lipids [213] . The approach utilizes the property
of naturally nucleus-occurring polyamine spermine, which is supposed to condense
DNA during cell division. By attaching a lipophilic anchor to spermine, dioctadecy-
lamidoglycylspermine (DOGS or Transfectan TM ) was prepared as the first cationic
lipid of this class of transfection vector ( Fig. 4.12 ) [213,214] .
It was observed that DOGS confer increased transfection efficacy as compared to
quaternary ammonium salts. Unlike quaternary ammonium salts, lipolymaine con-
denses DNA efficiently without the aid of any helper lipid for attaining significant
levels of transgene expression in vitro and in vivo. Succeeding developments were
made following DOGS [215] . With the objective of reducing side effects associated
with protein kinase C inhibition, tertiary amines are introduced instead of quarter-
nary amine. The lipoamine DC-Chol was presented with the tertiary amine linked
through a spacer to a cholesteryloxy-carbonyl lipid ( Fig. 4.12 ) [216] . In addition,
another aspect of this strategy was the introduction of different hydrophobic group
cholesteryl carbamate, which do not form bilayers but rather intercalate into bilayers
formed by DOPE. Because this DC-Chol does not confer enough compactness to
DNA, it could be coformulated with an additive lipid to obtain significant transfec-
tion level. DC-Chol complexes with DNA were the first to be used in clinical tri-
als [217,218] . Insufficient physicochemical characterization of DC-Chol complexes
prior to those trials does not justify the modest result obtained in terms of formula-
tion. Later, Lasic DD reported some physicochemical characterization of DC-Chol
complexes with DNA [219] .
Spermidine derivatives, pcTG 37, pcTG39, and T-shaped pcTG89 derived from
diaminopropionic acid were proposed as effective transfection vectors either alone or